I'm planning to visit Peru next month. While LP has 9-10 daily flights from Lima to Cuzco I've heard stories that it's a difficult flight to non-rev on. Would it be better to purchase a full-fare ticket or chance it non-reving?

If your travel plans are really flexible, then I would say non-rev. the money saved could go a long way and with 9-10 daily flights its hard for me to believe that you cant get a seat somewhere. What kind of planes do they fly between the two places?